Well I don't think pulling 4 Drones to kill the Engineering bay was necessary, you went pool first anyways...

Knowing that they were building a Planetary so quickly, if you didn't have a way to do damage before it finishes just Drone up, since you know they sacrificed any early attacks they might do to you. Especially if your Overlord had seen the third Command Center go up.

You know they are walling off the front with heavy defenses, and the most common harass method for Zerg is Mutalisks. But they already have an Engineering bay, you can bet they plan to be prepared for those, and with some Overlord scouting you can be certain.Drops or Swarm Hosts are pretty good alternatives.At the 12 minute mark the Terran had only 2 Marines as their whole army...

Just try not to let them get 12 Ravens with full energy with no resistance.

Also, if they aim a seeker missile at a Hydralisk/Roach, don't dance your whole army back and forth... grab the Hydralisk and send it off to die alone.